1. Field of the Invention
The present invention relates to a composite multilayer ceramic electronic part that is suitable for a multilayer circuit board including, for example, a microwave resonator, a filter or a multilayer capacitor, and to a method of manufacturing the same. Specifically, it relates to a composite multilayer ceramic electronic part comprising a laminate of a high dielectric-constant layer including a high dielectric-constant material with a low dielectric-constant layer including a low dielectric-constant material.
2. Description of the Related Art
Electronic equipment has become smaller in size, weight and thickness in recent years, and demands have been made to miniaturize electronic parts for use in such electronic equipment. However, conventional electronic part devices such as resonators are separately designed and constituted, and the miniaturization of these devices alone cannot sufficiently miniaturize the electronic equipment. Various multilayer ceramic substrates including electronic part devices such as capacitors or resonators inside thereof have therefore been proposed.
Such multilayer ceramic substrates must be further miniaturized and must be applied to signals of high frequency, and to this end, a variety of materials for composite multilayer substrates has been studied and proposed. Specifically, a variety of composite multilayer ceramic electronic parts including a low dielectric-constant layer and a high dielectric-constant layer have been proposed. In these ceramic electronic parts, a wiring is formed or a semiconductor device is mounted onto the low dielectric-constant layer. The high dielectric-constant layer is formed inside the low dielectric-constant layer, and comprises a material having a high dielectric constant and a low dielectric loss and thereby constitutes a capacitor or resonator. An example of these composite multilayer ceramic electronic parts is described in Japanese Unexamined Patent Application Publication No. 12-264724.
However, such composite multilayer ceramic electronic parts comprise a combination of a low dielectric-constant material and a high dielectric-constant material and thereby invite delamination in the interface between the two materials or deformation of the resulting substrates due to the difference in the shrinkage profile or in the thermal expansion coefficient between the two materials.
In high-frequency applications, Cu, Ag and other conductors which have a low electric resistance and a low melting point must be used. Accordingly, ceramic materials for use with these conductors must be fired at temperatures less than or equal to 1000xc2x0 C., since the ceramics must be integrally fired with these conductors having a low melting point.
The substrate materials must have a low dielectric loss for use in a microwave region, millimeter wave region and other high frequency regions. To yield a substrate material that can be fired at temperatures less than or equal to 1000xc2x0 C., it must further comprise a sintering aid such as glass in addition to a ceramic. However, sintering aids such as glass generally serve to increase the dielectric loss of the substrate material. For this reason, a substrate material, which can be fired at low temperatures of less than or equal to 1000xc2x0 C. and has a low dielectric loss, cannot significantly be obtained.
Under these circumstances, an object of the present invention is to provide a composite multilayer ceramic electronic part which is resistant to delamination or deformation in the interface between different types of materials, can be fired at low temperatures and is suitable for the high-frequency applications, and a method of manufacturing the multilayer composite ceramic electronic part.
Specifically, the present invention provides, in one aspect, a composite multilayer ceramic electronic part including a high dielectric-constant layer and at least one low dielectric-constant layer laminated with each other. The high dielectric-constant layer includes a high dielectric-constant material and has a relative dielectric constant xcex5r of equal to or more than about 20, and the low dielectric-constant layer includes a low dielectric-constant material and has a relative dielectric constant xcex5r of less than or equal to about 10. In this multilayer composite ceramic electronic part, the high dielectric-constant material mainly includes a BaOxe2x80x94TiO2xe2x80x94ReO3/2 dielectric and a first glass composition, where the BaOxe2x80x94TiO2xe2x80x94ReO3/2 dielectric is represented by the following formula: xBaOxe2x80x94yTiO2xe2x80x94zReO3/2, where x, y and z are % by mole and satisfy the following conditions: 8xe2x89xa6xxe2x89xa618; 52.5xe2x89xa6yxe2x89xa665; 20xe2x89xa6zxe2x89xa640; and x+y+z=100; and Re is a rare earth element, and the low dielectric-constant material includes a composite of a ceramic and a second glass composition.
By this configuration, the high dielectric-constant layer can constitute a capacitor or resonator using its high dielectric constant. In addition, the high dielectric-constant material yields a low dielectric loss in the high-frequency regions, specifically in the microwave region or millimeter wave region, due to crystallization of the glass composition, and thereby can constitute a capacitor or resonator having excellent high-frequency characteristics. The high dielectric-constant material can be fired at low temperatures of less than or equal to 1000xc2x0 C., and a conductor mainly comprising a metal having a low relative resistance such as gold, silver or copper can be used.
The low dielectric-constant layer has a low relative dielectric constant xcex5r of less than or equal to about 10 and can thereby constitute an insulator.
By using the combination of the high dielectric-constant layer and the low dielectric-constant layer, the present invention can provide a composite multilayer ceramic electronic part including a resonator or capacitor having excellent high-frequency characteristics.
The first glass composition in the high dielectric-constant material preferably includes about 10% to 25% by weight of SiO2, about 10% to 40% by weight of B2O3, about 25% to 55% by weight of MgO, 0% to about 20% by weight of ZnO, 0% to about 15% by weight of Al2O3, about 0.5% to 10% by weight of Li2O and 0% to about 10% by weight of RO, where R is at least one of Ba, Sr and Ca.
The high dielectric-constant material preferably further includes less than or equal to about 3% by weight of CuO and about 0.1% to 10% by weight of TiO2 based on the total weight of the high dielectric-constant material, as secondary components.
The high dielectric-constant material may include about 15% to 35% by weight of the first glass composition relative to about 65% to 85% by weight of the BaOxe2x80x94TiO2xe2x80x94ReO3/2 dielectric.
Preferably, the ceramic in the low dielectric-constant material is spinel (MgAl2O4), and the second glass composition includes about 30% to 50% by mole of silicon oxides in terms of SiO2, 0% to about 20% by mole of boron oxides in terms of B2O3, and about 20% to 55% by mole of magnesium oxide in terms of MgO.
The second glass composition preferably further includes less than or equal to about 30% by mole of at least one of CaO, SrO and BaO based on the total amount of the second glass composition.
The second glass composition preferably includes 0% to about 15% by mole of aluminum oxides in terms of Al2O3.
The second glass composition may further include less than or equal to about 10% by weight of at least one alkali metal oxide selected from Li2O, K2O and Na2O, based on the total weight of the second glass composition.
The low dielectric-constant material may further include less than or equal to about 3% by weight of copper oxides in terms of CuO based on the total weight of the low dielectric-constant material.
Preferably, the ceramic in the low dielectric-constant material is MgAl2O4, the second glass composition is a borosilicate glass, and an MgAl2O4 crystalline phase and at least one of an Mg3B2O6 crystalline phase and an Mg2B2O5 crystalline phase are precipitated as major crystalline phases in the low dielectric-constant layer.
In this case, the low dielectric-constant layer may include about 5% to 80% by weight of the MgAl2O4 crystalline phase and about 5% to 70% by weight of at least one of the Mg3B2O6 crystalline phase and the Mg2B2O5 crystalline phase.
Alternatively, the ceramic in the low dielectric-constant material may be MgAl2O4, the second glass composition may be a borosilicate glass, and an MgAl2O4 crystalline phase, an Mg2SiO4 crystalline phase, and at least one of an Mg3B2O6 crystalline phase and an Mg2B2O5 crystalline phase may be precipitated as major crystalline phases in the low dielectric-constant layer.
In this case, the low dielectric-constant layer may include about 5% to 80% by weight of the MgAl2O4 crystalline phase and about 5% to 70% by weight of the total of the Mg2SiO4 crystalline phase and at least one of the Mg3B2O6 crystalline phase and the Mg2B2O5 crystalline phase.
By these configurations, the low dielectric-constant material can be fired at low temperatures of less than or equal to 1000xc2x0 C. The high dielectric-constant layer and the low dielectric-constant layer can therefore integrally be fired at low temperatures of less than or equal to 1000xc2x0 C. and can further be co-fired with a conductor mainly including a metal having a low relative resistance, such as gold, silver or copper. In addition, the low dielectric-constant layer can yield a low dielectric loss in the high-frequency regions, specifically in the microwave region or millimeter wave region, due to crystallization of the glass composition as in the high dielectric-constant material and thereby yields a composite multilayer ceramic electronic part having further excellent high-frequency characteristics.
The borosilicate glass preferably includes about 8% to 60% by weight of boron oxides in terms of B2O3, about 10% to 50% by weight silicon oxides in terms of SiO2, and 10% to 55% by weight of magnesium oxide in terms of MgO.
The borosilicate glass may include 0% to about 20% by weight of at least one alkali metal oxide in terms of oxide.
In the low dielectric-constant material, the weight ratio of the ceramic and the second glass composition is preferably from about 20:80 to 80:20.
In the composite multilayer ceramic electronic part, the difference in the thermal expansion coefficient between the low dielectric-constant material and the high dielectric-constant material is preferably less than or equal to about 0.5 ppm/xc2x0C.
The present invention provides, in another aspect, a method of manufacturing a composite multilayer ceramic electronic part in which the composite multilayer ceramic electronic part includes a laminate of at least one high dielectric-constant layer having a relative dielectric constant of equal to or more than about 20 with at least one low dielectric-constant layer having a relative dielectric constant of less than or equal to about 10. The method includes the steps of preparing a laminate of at least one ply of a first ceramic green sheet with at least one ply of a second ceramic green sheet, and firing the laminate under such conditions that two plies of a third ceramic green sheet are pressed to and sandwich the top and bottom faces of the laminate. In this method, the first ceramic green sheet includes a composition of a high dielectric-constant material for constituting the high dielectric-constant layer, the second ceramic green sheet includes a composition of a low dielectric-constant material for constituting the low dielectric-constant layer, and the third ceramic green sheet includes a ceramic having a sintering temperature higher than the sintering temperatures of the low dielectric-constant material and the high dielectric-constant material.
By this configuration, the laminate can be prevented from shrinkage in an in-plane direction in the top and bottom faces thereof and thereby yields a composite multilayer ceramic electronic part having excellent dimensional precision.